I just recently replaced my DI resin in my 11 litre vessel (it had lasted me about 18 months before starting to creep up to ~30ppm, so time to change).Order some Tulsion MB-115 resin (struggled to find some in stock in December, but persevered), and replaced. First time I came to use it last weekend, I had the tap connected up and ran it through the vessel for a good 5 mins keeping an eye with my TDS meter, before I started rinsing the car, but the water didn't appear to drop below about 20ppm? (Previously when I've changed resin its been down to 0ppm).

So I'm wondering if

1. the TDS require any kind of calibration post battery change i.e. false reading?
2. does the resin require a longer period to work properly, or have I had the water pressure up too high so its gouged a channel through the resin rather than filtering to allow for efficient ion exchange?

Finally - when I was using my new woolly mammoth drying towel and pat drying post rinse, noted that the car wasn't completely dry after removing the towel (still some damp smears remaining)... and I did wash the towel prior to first use.